1. Field of the Invention
The present invention relates to a technique of a microscope, and more particularly, to a technique of an ultraviolet microscope for observing or examining a sample by using ultraviolet lights in a plurality of different wavelength bands.
2. Description of the Related Art
Conventionally, optical microscopes are widely used for fault examinations, structural observations, etc. of device patterns in semiconductor manufacturing processes. With the rapid advance in the shrinkages and the complexities of device patterns in recent years, the demand for improving the resolutions of optical microscopes has been increasing.
In order to meet such a demand, ultraviolet microscopes that implement a higher resolution by using an ultraviolet (UV) light as an illumination light as disclosed, for example, by Japanese unexamined patent application publication No. 2006-154237, and Japanese examined patent application publication No. 3324780 were developed. With such ultraviolet microscopes, a single UV light in a narrow wavelength band is used as an illumination light in many cases in order to avoid color aberration.
In the meantime, materials such as aluminum, copper, etc. used for semiconductor devices, etc. have reflectivities and absorption rates, which differ against ultraviolet lights in different wavelength bands. It is essential to use this characteristic in the above described fault examinations and structural analyses.
Specifically, a device material can be identified based on the degree of change when a semiconductor device is observed, for example, by changing the wavelength band of an ultraviolet light used for illumination, and by obtaining a change in the reflectivity of the device material with the detection of a change in a pixel value (the brightness value of each pixel) of an observation image at the time of observation.
A microscope system having a function to irradiate ultraviolet lights in a plurality of wavelength bands, a function to capture the image of a sample, and a function to display the captured image of the sample is required to identify a device material with the above described technique. Here, such a microscope system is referred to as a “multiband UV microscope system”.
Unlike conventional UV microscopes, the multiband UV microscope changes the wavelength band of an illumination light, and obtains observation images in a plurality of wavelength bands. Highlighting differences of the observation images respectively obtained by switching the wavelength band of the illumination light is essential to an observer so that he or she can easily identify the characteristic of a sample material only at a glance of an observation image.